1. Field of the Invention
This invention relates to a method for paging users in mobile communication system, and more particularly to a method of paging users using point-to-multipoint group for multimedia broadcast/multicast service in mobile communication system.
2. Description of the Related Art
(1) Basic Operation Process of Existing Paging
Paging in existing communication system is a point-to-point user-based paging, whose basic operation process is shown in FIG. 3:
After a mobile terminal is registered in the network, it will be distributed to a paging group. There is a Paging Indicator (hereinafter referred to as PI) 204 for each paging group. When a terminal belonging to a paging group is paged, PI corresponding to this paging group will appear on the Paging indicator Channel (hereinafter referred to as PICH) 202 cyclically.
When the terminal detects its PI on PICH, it will start to receive specific paging message from Secondary Common Control Physical Channel (hereinafter referred to as SCCPCH) 201. In other words, PICH only carries PI information, and paging message is carried by SCCPCH. The explanation for paging message is the upper layer function of User Equipment (UE) protocol.
In order to decrease power consumption, terminal is designed as Discrete Receiving (hereinafter referred to as DRX) mode, i.e. terminal stays in sleep mode when it is in idle mode. In this mode, Terminal will consume less power. Only when terminal detects its PI, terminal will be woken up to receive specific paging message.
PI monitoring by terminal is also cyclical, and the length of the cycle is determined by the network. The larger the cycle is, the less possibly terminal wakes up from sleep, and thus the longer terminal battery standby time will be, but the cost is to reduce the response speed of terminal to network paging.
(2) Frame Structure of Existing PICH
PICH is the pure-physical channel used to carry PI, and has been described in detail in 3 GPP specification TS 25.211 v4.2.0. FIG. 4 shows its frame structure.
The length of a PICH wireless frame is 10 ms, and the frame is composed of 300 bits, in which 288 bits are used to carry PI and the remaining 12 bits are reserved for future use and won't be transmitted. A Paging Indicator (PI) is composed of several bits. According to the different length of PI, a PICH frame can carry 18, 36, 72 or 144 PIs. Np indicates the number of PIs in a PICH frame.
The position of PI in a frame is calculated according to International Mobile Subscriber Identity number (hereinafter referred to as IMSI) of the subscriber, and the calculation method is as follows:
PI=DRX Index mod Np. Wherein DRX Index equals to IMSI div 8192. “mod” indicates the modulus operation, and “div” indicates round-off operation for division.
To guarantee reliable transmission, existing technology deploys the following SFN based sliding mechanism:
  q  =            (              PI        +                  ⌊                                    (                                                (                                      18                    ×                                          (                                              SFN                        +                                                  ⌊                                                      SFN                            /                            8                                                    ⌋                                                +                                                  ⌊                                                      SFN                            /                            64                                                    ⌋                                                +                                                  ⌊                                                      SFN                            /                            512                                                    ⌋                                                                    )                                                        )                                ⁢                mod                ⁢                                                                  ⁢                144                            )                        ×                          Np              144                                ⌋                    )        ⁢    modNp  In above equation, “q” indicates the actual position of PI in a frame, and SFN is the system frame number, which changes with time. With the change of SFN, the position of PI, i.e. q, will slide. └ ┘indicates round-off operation and “mod” indicates modulus operation.“Pq” is used to indicate the value of PI on the position of q. If Pq equals 1, it is indicated that PI is valid and UE shall be woken up to read paging message; if Pq equals 0, it is indicated that PI is invalid and it is unnecessary for UE to be woken up to read paging message. The mapping relation between paging indicator Pq, and PICH is shown in following table (Table 1):
TABLE 1Mapping relation between paging indicator.Pq and PICH bitsNumber of PIs in each frame (Np)Pq = 1Pq = 0Np = 18{b16q, . . ., b16q + 15} = {−1, −1, . . ., −1}{b16q, . . ., b16q + 15} = {+1, +1, . . ., +1}Np = 36{b8q, . . ., b8q+7} = {−1, −1, . . ., −1}{b8q, . . ., b8q+7} = {+1, +1, . . ., +1}Np = 72{b4q, . . ., b4q+3} = {−1, −1, . . ., −1}{b4q, . . ., b4q+3} = {+1, +1, . . ., +1}Np = 144{b2q, b2q+1} = {−1, −1}{b2q, b2q+1} = {+1, +1}
It is seen from Table 1 that when Pq=1, all bits composing the PI shall be set as ‘−1’ and when Pq=0, those shall be all set as ‘+1’.
(3) Frame Structure of Existing PCH IubFP
Since paging is initiated by the network, paging information must be transferred to the air interface via proper mode for the convenience of receiving by terminal. FIG. 5 shows the frame structure of existing PCH's Node B and Radio Network Controller interface frame protocol (hereinafter referred to as PCH IubFP). PCH IubFP is used to transfer paging information between base station (hereinafter referred to as Node B) and Radio Network Controller (hereinafter referred to as RNC). 3 GPP specification TS25.435 v4.2.0 has given detailed description for existing PCH IubFP frame structure.
PCH IubFP frame includes PI information and paging message. To page a UE, two continuous PCH IubFP frames will be used. The first frame includes PI information and the second includes paging message. Descriptions for the components shown in FIG. 5 are as follows:                Paging Indicator (PI)        
Description: Indicate whether this frame has PI-bitmap or not.
Value range: {0=the absence of PI-bitmap; 1=the presence of PI-bitmap }.
Field length: 1 bit                PI bitmap (PI-bitmap)        
Description: Indicate the bitmaps of PI0 . . . PIN-1. The 7th bit of the first byte includes PI0, and the 6th bit includes PI1; The 7th bit of the second byte includes PI8, and so on.                Value range: {18, 36, 72, 144 PIs.}.        Field length: 3, 5, 9, or 18 bytes        
(4) Flow of Existing Paging and Radio Bearer Setup
3 GPP specification TS 23.846 v1.1.0 describes the MBMS service paging and radio bearer setup process. FIG. 6 shows the signalling flow of paging and radio bearer setup. Detailed descriptions for each step of the flow are given in the following.    601 BM-SC sends data to SGSN via GGSN.    602 SGSN sends “MBMS notification” to UTRAN to indicate that a certain MBMS service will be started.    603 UTRAN sends “MBMS notification” to UE in MBMS service area.    604 UTRAN sends a “MBMS service request” message to SGSN to request service.    605 and 606 establish radio access bearer (hereinafter referred to as RAB) between UTRAN and SGSN.    607 UE that has activated MBMS service sends a “MBMS radio request” message to the network after receiving “MBMS notification”.    608 UTRAN establishes radio bearer (hereinafter referred to as RB) over the air-interface and sends a “MBMS radio allocation” message to UE.    609 After all radio resources are established successfully, data transfer can be performed.    610 Release all network resources after finishing data transmission.
According to FIG. 6, paging process 603 and radio bearer setup process 608 are performed independently.
(5) Existing Paging Message
In 3 GPP specification TS25.331 v4.2.0, existing paging message is called “Paging Type 1”. When UE needs to be paged, Radio Network Controller (hereinafter referred to as RNC) sends “Paging Type 1” message to UE via base station (hereinafter referred to as Node B).
This message includes information on following several aspects:                Paging record list listing the identity of UE that is paged by the message.        Broadcast Control Channel modification info (BCCH modification info) representing Modification indication for system broadcast information.        
One paging message can include paging records for multiple UEs, which are known as “Paging record”. Paging Record (Paging Record) includes following several parameters:                Paging cause representing the cause of initiating the paging. At present, causes listed in the specification are as follows:        Conversational Call (Terminating Conversational Call)        Streaming Call (Terminating Streaming Call)        Interactive Call (Terminating Interactive Call)        Background Call (Terminating Background Call)        High Priority Signalling (Terminating High Priority Signalling)        Low Priority Signalling (Terminating Low Priority Signalling)        Cause Unknown (Terminating—cause unknown)        UE Identity (UE Identity) representing the identity of UE, which can be International Mobile Subscriber Identity (IMSI), Temporary Mobile Subscriber Identity (TMSI), Packet-Temporary Mobile Subscriber Identity (P-TMSI), UE-Radio Network Temporary Identity (U-RNTI), etc. UE confirms self-paging through checking the UE identity.        